MFC r274711:

Stop using early_putc immediately after configuring console with cninit()

MFC r276532 and r276626:
The "cnputs_mtx" mutex must be allowed to recurse. Debug prints and/or
witness printouts in the console driver clients can cause this mutex
to recurse by calls to "printf()" from witness for example. In
particular this can happen if "debug.witness.skipspin=0" is set in the
boot environment.

MFC automatic vt(4) selection for UEFI boot

r268158: Prefer vt(4) for UEFI boot

The UEFI framebuffer driver vt_efifb requires vt(4), so add a
mechanism for the startup routine to set the preferred console.
This change is ugly because console init happens very early in the
boot, making a cleaner interface difficult. This change is intended
only to facilitate the sc(4) / vt(4) transition, and can be reverted
once vt(4) is the default.

r268160: Fix typos in VTY constant names from r268158

r268982: Don't pass null kmdp to preload_search_info

On Xen PVH guests kmdp == NULL.

Sponsored by: The FreeBSD Foundation

MFC part of r267973: remove redundant "" assignment for string in BSS.

Sponsored by: The FreeBSD Foundation

267622 Log:
Rename vt(4) vga module to dismiss interference with syscons(4) vga module.
267623 Log:
Remove stale link to deleted vt(4) xboxfb driver.
267624 Log:
syscons(4) and vt(4) can be built together now.
267625 Log:
Allow to disable syscons(4) if "hw.syscons.disable" kenv is set.
267626 Log:
Suspend vt(4) initialization if "kern.vt.disable" kenv is set.
267965 by emaste@ Log:
Use a common tunable to choose between vt(4)/sc(4)
With this change and previous work from ray@ it will be possible to put
both in GENERIC, and have one enabled by default, but allow the other to
be selected via the loader.
(The previous implementation had separate kern.vt.disable and
hw.syscons.disable tunables, and would panic if both drivers were
compiled in and neither was explicitly disabled.)
268175 by emaste@ Log:
Fix vt(4) detection in kbdcontrol and vidcontrol
As sc(4) and vt(4) coexist and are both enabled in GENERIC, the existence
of a vt(4) sysctl is not sufficient to determine that vt(4) is in use.
Reported by: Trond Endrestøl
268045 by emaste@ Log:
Add vt(4) to GENERIC and retire the separate VT config
vt(4) and sc(4) can now coexist in the same kernel. To choose the vt
driver, set the loader tunable kern.vty=vt .

Sponsored by: The FreeBSD Foundation

MFC r261786, r261789

Rework the EARLY_PRINTF mechanism. Instead of defining a special eprintf()
routine, now a platform can provide a pointer to an early_putc() routine
which is used instead of cn_putc(). Control can be handed off from early
printf support to standard console support by NULLing out the pointer
during standard console init.

Convert two while(1); statements into proper panics.

MFC r260118

Delete echoed doesn't rub out the previous character, so always
use <backspace> <space> <backspace> instead. This fixes hitting
DELETE instead of BACKSPACE at mountroot> prompt.

MFC r274711:

Stop using early_putc immediately after configuring console with cninit()

MFC r276532 and r276626:
The "cnputs_mtx" mutex must be allowed to recurse. Debug prints and/or
witness printouts in the console driver clients can cause this mutex
to recurse by calls to "printf()" from witness for example. In
particular this can happen if "debug.witness.skipspin=0" is set in the
boot environment.

MFC automatic vt(4) selection for UEFI boot

r268158: Prefer vt(4) for UEFI boot

The UEFI framebuffer driver vt_efifb requires vt(4), so add a
mechanism for the startup routine to set the preferred console.
This change is ugly because console init happens very early in the
boot, making a cleaner interface difficult. This change is intended
only to facilitate the sc(4) / vt(4) transition, and can be reverted
once vt(4) is the default.

r268160: Fix typos in VTY constant names from r268158

r268982: Don't pass null kmdp to preload_search_info

On Xen PVH guests kmdp == NULL.

Sponsored by: The FreeBSD Foundation

MFC part of r267973: remove redundant "" assignment for string in BSS.

Sponsored by: The FreeBSD Foundation

267622 Log:
Rename vt(4) vga module to dismiss interference with syscons(4) vga module.
267623 Log:
Remove stale link to deleted vt(4) xboxfb driver.
267624 Log:
syscons(4) and vt(4) can be built together now.
267625 Log:
Allow to disable syscons(4) if "hw.syscons.disable" kenv is set.
267626 Log:
Suspend vt(4) initialization if "kern.vt.disable" kenv is set.
267965 by emaste@ Log:
Use a common tunable to choose between vt(4)/sc(4)
With this change and previous work from ray@ it will be possible to put
both in GENERIC, and have one enabled by default, but allow the other to
be selected via the loader.
(The previous implementation had separate kern.vt.disable and
hw.syscons.disable tunables, and would panic if both drivers were
compiled in and neither was explicitly disabled.)
268175 by emaste@ Log:
Fix vt(4) detection in kbdcontrol and vidcontrol
As sc(4) and vt(4) coexist and are both enabled in GENERIC, the existence
of a vt(4) sysctl is not sufficient to determine that vt(4) is in use.
Reported by: Trond Endrestøl
268045 by emaste@ Log:
Add vt(4) to GENERIC and retire the separate VT config
vt(4) and sc(4) can now coexist in the same kernel. To choose the vt
driver, set the loader tunable kern.vty=vt .

Sponsored by: The FreeBSD Foundation

MFC r261786, r261789

Rework the EARLY_PRINTF mechanism. Instead of defining a special eprintf()
routine, now a platform can provide a pointer to an early_putc() routine
which is used instead of cn_putc(). Control can be handed off from early
printf support to standard console support by NULLing out the pointer
during standard console init.

Convert two while(1); statements into proper panics.

MFC r260118

Delete echoed doesn't rub out the previous character, so always
use <backspace> <space> <backspace> instead. This fixes hitting
DELETE instead of BACKSPACE at mountroot> prompt.